This invention relates generally to a combination microwave oven and exhaust vent or ventilator appliance, and more particularly to an air flow system for the combination.
Combination microwave oven and conventional range systems are well known in the art. Many manufacturers of major appliances market such systems. One popular system is comprised of a unitary structure having a traditional electric range mounted in a lower portion and a microwave oven mounted in an upper portion. Another popular combination is that of a traditional gas or electric range adapted to accommodate a microwave generating system in the same oven cavity. More recently, a number of major appliance manufacturers have marketed a microwave oven adaptable for installation above and separate from a traditional range. These microwave ovens utilize the space formerly allocated to the range hood ventilation system, and have been modified or adapted to accommodate the functions formerly provided by the exhaust vents.
Because these combination microwave oven and exhaust vents or ventilators are designed to accomplish the purposes originally accomplished by two appliances, compromises have been made. Significant compromises have also been required in light of the limited space generally available above a range, cooktop or grille, such cooking surfaces normally being approximately 30" wide. For example, most ceilings are only 8' high with the kitchen in many homes designed to place cabinets above the lower cooking surface. Traditional vent hoods or ventilators have been designed to adapt to or coordinate with these kitchen cabinets, placing the hood far enough away from the cooking surface to allow easy access to the heating elements and the controls, yet close enough to remove the hot, frequently greasy, air rising from the lower cooking surface.
As a result of these space limitations in particular, the prior art attempts to provide for an overhead mounting of a microwave oven, or the combination of a microwave oven with a ventilator, have heretofore required compromises in the microwave oven, the ventilating system, or both. Some such compromises have resulted in smaller-than-usual microwave oven cooking cavities to allocate greater space to the ventilator portion of the system. One example will be noted in U.S. Pat. No. 4,254,450 to White et al, issued Mar. 3, 1981. Other systems have attempted to retain most of the advantages and size of a typical countertop microwave oven by reducing the air handling capability of the ventilating portion of the combination appliances.
A major design consideration for such combination appliances, particularly in view of the space limitations, is the maintenance of the separate air circulation systems that microwave ovens and ventilation hoods normally require or exhibit. Specifically, the microwave oven portion of such a system requires a quantity of air to cool the high voltage compartment. It also requires, in the case of an air driven microwave stirrer or antenna distribution system, a source of air movement to rotate the energy distribution system. Lastly, it has generally been found to be preferable in the operation of a microwave oven to circulate air past the door to remove any steam condensed thereon. This improves the visibility in the oven cavity. All of the above-mentioned requirements for air are for relatively dry, cool and clean air.
Cool, uncontaminated air is generally not what rises from the surface of a conventional range, cooktop or grille when in operation. The process of cooking, by its very nature, vaporizes quantities of water and grease, creating much of the air which a ventilation hood removes due to the heat expansion of the air. Water, for example, expands approximately 1800 times when it becomes steam. It is primarily this hot, grease-laden air that rises from the cooking surface and is exhausted by a ventilator. Hence, the operation of the ventilator portion of a combination system in removing the hot, grease-laden air rising from the cooking surface is not necessarily compatible with the microwave oven portion. The problems are compounded by the fact that the exhaust vent itself requires a certain amount of cool, dry and clean air to ensure its long life and serviceability.